In order to improve the performance of internal combustion engines, not only in the terms of specific output and fuel economy, but also so as to increase the exhaust emission control, a variety of types of control systems have been proposed. One particularly effective control system employs a sensor that senses the air/fuel ratio in the combustion chamber. By utilizing the output of this sensor, it is possible to make finite adjustments in the fuel and air control to maintain the desired fuel/air ratio.
The sensors normally utilized for this purpose are of a type which generally require them to be at a predetermined temperature in order to provide a reliable output. For example, a sensor commonly used for this purpose is an oxygen (O.sub.2) sensor. These oxygen sensors sense the amount of oxygen in the combustion products. By sensing the amount of oxygen present in the combustion products, it is possible to accurately determine the fuel/air ratio. Of course, this type of sensor must be at the proper operating temperature to provide a reliable output.
The use of oxygen sensors for engine control in relationship to two-cycle engines presents a significant problem. With a two-cycle engine, unlike four-cycle engines, there is a risk that the combustion products that are sampled may not be pure combustion products. That is, with a two-cycle engine there is a time during the scavenging cycle when the combustion products may become mixed with a fresh charge. If this occurs, then improper readings will be generated and engine control will not be successful.
Therefore, there have been proposed systems wherein the sensor communicates with the engine combustion chamber through a port and at such a time when primarily pure combustion products will be in the combustion chamber. This means that the sensor is not exposed continuously to the hot combustion gases.
Therefore, there is a risk with this type of installation that the sensor can cool between successive readings and the output signal can become unreliable.
It is, therefore, a principal object of this invention to provide an improved arrangement for communicating a combustion condition sensor with the combustion chamber of an engine.
It is a further object of this invention to provide a combustion condition sensor that is insulated so that it will maintain its temperature between successive samplings.
It is a still further object of this invention to provide an improved sensor arrangement for an engine wherein the path that delivers the combustion products to the sensor and the sensor itself is configured to ensure the maintenance of the operating temperature of the sensor.